Making imprinted multi-layer biocidal particle structure

ABSTRACT

A method of making a multi-layer biocidal structure includes providing a support and locating a first curable layer on the support. A second curable layer is located on the first curable layer, the second curable layer having multiple biocidal particles dispersed within the second curable layer. The first curable layer and the second curable layer are imprinted in a single step with an imprinting stamp having a structure with a depth greater than the thickness of the second curable layer. The first curable layer and the second curable layer are cured in a single step to form a first cured layer and a second cured layer. The imprinting stamp is removed.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned co-pending U.S. patentapplication Ser. No. 14/526,595, filed Oct. 29, 2014, entitled ImprintedMulti-layer Structure, by Cok et al, to commonly-assigned U.S. patentapplication Ser. No. 14/526,603 (now U.S. Pat. No. 9,186,698) filed Oct.29, 2014, entitled Making Imprinted Multi-layer Structure, by Cok et al,to commonly-assigned co-pending U.S. patent application Ser. No.14/526,611, filed Oct. 29, 2014, entitled Imprinted Multi-layer BiocidalParticle Structure, by Cok et al, to commonly-assigned co-pending U.S.patent application Ser. No. 14/526,640, filed Oct. 29, 2014, entitledUsing Imprinted Multi-layer Biocidal Particle Structure, by Cok et al,to commonly-assigned co-pending U.S. patent application Ser. No.14/526,646, filed Oct. 29, 2014, entitled Imprinted Particle Structure,by Cok et al, to commonly-assigned co-pending U.S. patent applicationSer. No. 14/526,666, filed Oct. 29, 2014, entitled Making ImprintedParticle Structure, by Cok et al, to commonly-assigned co-pending U.S.patent application Ser. No. 14/526,691, filed Oct. 29, 2014, entitledUsing Imprinted Particle Structure, by Cok et al, and tocommonly-assigned co-pending U.S. patent application Ser. No.14/519,451, filed Oct. 21, 2014, entitled Making Colored BiocidalMulti-Layer Structure, by Scheible et al, the disclosures of which areincorporated herein.

FIELD OF THE INVENTION

The present invention relates to biocidal layers having antimicrobialefficacy on a surface.

BACKGROUND OF THE INVENTION

Widespread attention has been focused in recent years on theconsequences of bacterial and fungal contamination contracted by contactwith common surfaces and objects. Some noteworthy examples include thesometimes fatal outcome from food poisoning due to the presence ofparticular strains of Escherichia coli in undercooked beef; Salmonellacontamination in undercooked and unwashed poultry food products; as wellas illnesses and skin irritations due to Staphylococcus aureus and othermicro-organisms. Anthrax is an acute infectious disease caused by thespore-forming bacterium bacillus anthracis. Allergic reactions to moldsand yeasts are a major concern to many consumers and insurance companiesalike. In addition, significant fear has arisen in regard to thedevelopment of antibiotic-resistant strains of bacteria, such asmethicillin-resistant Staphylococcus aureus (MRSA) andvancomycin-resistant Enterococcus (VRE). The U.S. Centers for DiseaseControl and Prevention estimates that 10% of patients contractadditional diseases during their hospital stay and that the total deathsresulting from these nosocomially-contracted illnesses exceeds thosesuffered from vehicular traffic accidents and homicides. In response tothese concerns, manufacturers have begun incorporating antimicrobialagents into materials used to produce objects for commercial,institutional, residential, and personal use.

Noble metal ions such as silver and gold ions are known for theirantimicrobial properties and have been used in medical care for manyyears to prevent and treat infection. In recent years, this technologyhas been applied to consumer products to prevent the transmission ofinfectious disease and to kill harmful bacteria such as Staphylococcusaureus and Salmonella. In common practice, noble metals, metal ions,metal salts, or compounds containing metal ions having antimicrobialproperties can be applied to surfaces to impart an antimicrobialproperty to the surface. If, or when, the surface is inoculated withharmful microbes, the antimicrobial metal ions or metal complexes, ifpresent in effective concentrations, will slow or even preventaltogether the growth of those microbes. Recently, silver sulfate,Ag₂SO₄, described in U.S. Pat. No. 7,579,396, U.S. Patent ApplicationPublication 2008/0242794, U.S. Patent Application Publication2009/0291147, U.S. Patent Application Publication 2010/0093851, and U.S.Patent Application Publication 2010/0160486 has been shown to provideefficacious antimicrobial protection in polymer composites. The UnitedStates Environmental Protection Agency (EPA) evaluated silver sulfate asa biocide and registered its use as part of EPA Reg. No, 59441-8 EPAEST. NO. 59441-NY-001. In granting that registration, the EPA determinedthat silver sulfate was safe and effective in providing antibacterialand antifungal protection.

Antimicrobial activity is not limited to noble metals but is alsoobserved in other metals such as copper and organic materials such astriclosan, and some polymeric materials.

It is important that the antimicrobial active element, molecule, orcompound be present on the surface of the article at a concentrationsufficient to inhibit microbial growth. This concentration, for aparticular antimicrobial agent and bacterium, is often referred to asthe minimum inhibitory concentration (MIC). It is also important thatthe antimicrobial agent be present on the surface of the article at aconcentration significantly below that which can be harmful to the userof the article. This prevents harmful side effects of the article anddecreases the risk to the user, while providing the benefit of reducingmicrobial contamination. There is a problem in that the rate of releaseof antimicrobial ions from antimicrobial films can be too facile, suchthat the antimicrobial article can quickly be depleted of antimicrobialactive materials and become inert or non-functional. Depletion resultsfrom rapid diffusion of the active materials into the biologicalenvironment with which they are in contact, for example, water solublebiocides exposed to aqueous or humid environments. It is desirable thatthe rate of release of the antimicrobial ions or molecules be controlledsuch that the concentration of antimicrobials remains above the MIC. Theconcentration should remain there over the duration of use of theantimicrobial article. The desired rate of exchange of the antimicrobialcan depend upon a number of factors including the identity of theantimicrobial metal ion, the specific microbe to be targeted, and theintended use and duration of use of the antimicrobial article.

Antimicrobial coatings are known in the prior art, for example asdescribed in U.S. Patent Application Publication No. 2010/0034900. Thisdisclosure teaches a method of coating a substrate with biocideparticles dispersed into a coating so that the particles are in contactwith the environment. Non-planar coatings are also known to providesurface topographies for non-toxic bio-adhesion control, for example asdisclosed in U.S. Pat. No. 7,143,709.

Imprinting methods useful for forming surface topographies are taught inCN102063951. As discussed in CN102063951, a pattern of micro-channelsare formed in a substrate using an embossing technique. Embossingmethods are generally known in the prior art and typically includecoating a curable liquid, such as a polymer, onto a rigid substrate. Apattern of micro-channels is embossed (impressed or imprinted) onto thepolymer layer by a master having an inverted pattern of structuresformed on its surface. The polymer is then cured.

Fabrics or materials incorporating biocidal elements are known in theart and commercially available. U.S. Pat. No. 5,662,991 describes abiocidal fabric with a pattern of biocidal beads. U.S. Pat. No.5,980,620 discloses a means of inhibiting bacterial growth on a coatedsubstrate comprising a substantially dry powder coating containing abiocide. U.S. Pat. No. 6,437,021 teaches a water-insoluble polymericsupport containing a biocide. Methods for depositing thinsilver-comprising films on non-conducting substrates are taught in U.S.Patent Application Publication No. 2014/0170298.

SUMMARY OF THE INVENTION

The efficacy of antimicrobial coatings and materials depend at least inpart on their structure and surface area. The cost of the coatings alsodepends upon the quantity of materials in the coatings. There is a need,therefore, for antimicrobial coatings with improved efficacy and reducedcosts.

In accordance with the present invention, a method of making amulti-layer biocidal structure includes:

providing a support;

locating a first curable layer on the support;

locating a second curable layer on the first curable layer, the secondcurable layer having multiple biocidal particles dispersed within thesecond curable layer;

imprinting the first curable layer and the second curable layer in asingle step with an imprinting stamp having a structure with a depthgreater than the thickness of the second curable layer;

curing the first curable layer and the second curable layer in a singlestep to form a first cured layer and a second cured layer; and

removing the imprinting stamp.

The present invention provides a biocidal multi-layer structure thatprovides improved antimicrobial properties with thinner layers havingincreased surface area made in a cost-efficient process.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent when taken in conjunction with the followingdescription and drawings wherein identical reference numerals have beenused to designate identical features that are common to the figures, andwherein:

FIG. 1 is a cross section of a multi-layer structure illustrating anembodiment of the present invention;

FIGS. 2A and 2B are cross sections of multi-layer structures in otherembodiments of the present invention;

FIG. 3 is a cross section of a multi-layer structure including particlesin an embodiment of the present invention;

FIGS. 4A-4F are cross sections of sequential construction steps usefulin a method of the present invention;

FIGS. 5A-5F are cross sections of sequential construction steps usefulin another method of the present invention;

FIGS. 6A-6D are cross sections of sequential construction steps usefulin yet another method of the present invention;

FIG. 7 is a flow diagram illustrating a method of the present invention;

FIGS. 8A and 8B are flow diagrams illustrating alternative methods ofthe present invention; and

FIG. 9 is a flow diagram illustrating another method of the presentinvention.

The Figures are not drawn to scale since the variation in size ofvarious elements in the Figures is too great to permit depiction toscale.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a multi-layer structure useful in formingan antimicrobial article on a support. Multi-layer structures of thepresent invention provide improved antimicrobial properties with thinnerlayers having increased surface area made in a cost-efficient process.In useful methods of the present invention, multiple uncured coatingsare formed on a support, imprinted together, and then cured together. Athin top layer can include reduced quantities of antimicrobial materialsor antimicrobial particles. The imprinted layers provide a greatersurface area for the antimicrobial materials and a topographicalstructure that inhibits the growth and reproduction of microbes. Coatingand imprinting processes provide a cost-efficient manufacturing method.

Referring to FIG. 1, in an embodiment of the present invention, animprinted multi-layer structure 5 includes a support 30 having a supportthickness 36. A bi-layer 7 having a topographical structure is locatedon or over the support 30. The structured bi-layer 7 includes a firstcured layer 10 including a first cross-linked material on or over thesupport 30 and a second cured layer 20 including a second materialdifferent from the first material on or over the first cured layer 10 ona side of the first cured layer 10 opposite the support 30. The firstcured layer 10 has a first cured layer thickness 16 and the second curedlayer 20 has a second-layer thickness 26. Indentations 80 are located inthe first and second cured layers 10, 20 to form a topographicalstructure with a depth 46. The first material of the first cured layer10 is cross-linked to the second material of the second cured layer 20and the depth 46 of the bi-layer 7 structure is greater than thesecond-layer thickness 26 of the second cured layer 20. Coating or otherdeposition methods for forming multiple layers on a substrate are knownin the art, as are imprinting methods useful for forming theindentations 80 in the first and second cured layers 10, 20.

In an embodiment, the second cured layer 20 is thinner than the firstcured layer 10. As shown in FIG. 1, the first cured layer 10 hasportions with the first-layer thickness 16 that are thicker than thesecond-layer thickness 26.

As used herein, a structured layer is a layer that is not smooth or notplanar on a microscopic scale corresponding to the magnitude of theindentations 80. For example if the support 30 is planar, a structuredlayer formed on the support 30 according to the present invention isflat but non-planar and is not smooth. If the support 30 is not planarbut is smooth, for example having a surface that is curved in one ormore dimensions (such as a spherical section), a structured layer formedon the support 30 according to the present invention is also non-planarbut is not smooth. Whether or not the support 30 is planar, thestructured layer can include indentations 80, channels, pits, holes,extended portions, mesas or other physical elements or structures. Inone embodiment, the surface is rough. The structure depth 46 of thestructured bi-layer 7 is the distance from the portion of the structuredbi-layer 7 furthest from the support 30 to the portion of the structuredbi-layer 7 that is closest to the support 30 in a direction that isorthogonal to a surface of the support 30.

In an embodiment, the first cured layer 10 is located on or over thesupport 30. The support 30 is any layer that is capable of supportingthe first and second cured layers 10, 20 and in different embodiments isrigid, flexible, or transparent and, for example is a substrate made ofglass, plastic, paper, or vinyl or combinations of such materials orother materials. In an embodiment, the first cured layer 10 is crosslinked to the second cured layer 20 to provide rigidity and improvedstrength for the layers.

In a useful arrangement, the support 30 is adhered, for example with anadhesive layer 50 such as a pressure-sensitive adhesive or glue such aswall-paper glue, to a surface 8 of a structure 40. The surface 8 is anysurface 8, planar or non-planar that is desired to resist the growth ofbiologically undesirable organisms, including microbes, bacteria, orfungi. In various applications, the structure 40 is a structure such asa wall, floor, table top, door, handle, cover, device, or any structure40 having the surface 8 likely to come into contact with a human. Theimprinted multi-layer structure 5 can form a wall paper or plastic wrapfor structures 40.

In an embodiment of the present invention, the second cured layer 20includes a second material that is different from the first cross-linkedmaterial in the first cured layer 10. In another embodiment of thepresent invention, the second material includes a second cross-linkedmaterial that is the same as the first cross-linked material. In thisembodiment, either the first cross-linked material includes a thirdmaterial that is not in the second cross-linked material or the secondcross-linked material includes a third material that is not in the firstcross-linked material. Therefore, the first cross-linked material andsecond material are different or include different materials.

In one embodiment, the second cured layer 20 is electrically conductiveand the first cured layer 10 is electrically insulating. Electricallyconductive materials, for example polyethyldioxythiophene (PEDOT) areknown in the art, as are insulating polymers or resins. In anembodiment, the second cured layer 20 is electrically conductive.

Referring to FIG. 2A, in another embodiment the second cured layer 20(FIG. 1) is chemically patterned to form a patterned second cured layer21 that has conductive portions 21 a and non-conductive portions 21 b.Materials and methods for pattern-wise inhibiting the electricalconductivity of PEDOT are known. By patterning such inhibiting chemicalsover the extent of the second cured layer 20 (FIG. 1), the electricalconductivity of the second cured layer 20 is likewise patterned to formthe patterned second cured layer 21 with conductive portions 21 a andnon-conductive portions 21 b.

As shown in FIG. 2A in a further embodiment, a binder primer 52 islocated between the first cured layer 10 and the support 30. The binderprimer 52 can be an adhesive layer 50 that adheres the first cured layer10 to the support 30. Alternatively, or in addition, the binder primer52 can form a support surface on which the first cured layer 10 isreadily coated, for example by controlling the surface energy of thesupport surface or the first cured layer 10. In another embodiment notshown in FIG. 1 or 2, the binder primer 52 or the adhesive 50 is locatedbetween the first cured layer 10 and the second cured layer 20 or thepatterned second cured layer 21 to adhere the first cured layer 10 andthe second cured layers 20 or the patterned second cured layer 21together and enable the second cured layer 20 or the patterned secondcured layer 21 to be coated over the first cured layer 10 before thefirst cured layer 10 and the second cured layer 20 or the patternedsecond cured layer 21 are imprinted to form the indentations 80 of thebi-layer 7 and the imprinted multi-layer structure 5.

In a useful arrangement illustrated in FIG. 2B, the indentations 80 ofthe bi-layer 7 contain a third cured material 42, for exampleelectrically conductive material that forms an electrical conductor. Inan embodiment, such an electrically conductive third cured material 42is formed by coating a liquid conductive link, for example containingmetallic nano-particles, over the surface of the structured bi-layer 7,removing the conductive ink from surface portions of the structuredbi-layer 7 leaving remaining conductive link in the indentations 80, andcuring the liquid conductive link to form electrical conductors.Suitable liquid conductive inks are known in the art and areelectrically conductive after curing. In another embodiment, theconductivity of the third cured material 42 is greater than theconductivity of the second cured layer 20 or the patterned second curedlayer 21.

A combination of the electrically conductive third cured material 42 andthe patterned second cured layer 21 with conductive portions 21 a andnon-conductive portions 21 b can form an electrical circuit or patternedconductor. The electrical circuit can electrically connect separatedelectrical conductors in the indentations 80 or can include separatecircuits in the indentations 80 and the patterned second cured layer 21.The electrical circuit can connect electronic computing devices such asintegrated circuits (not shown).

Referring to FIG. 3 in another useful embodiment of the imprintedmulti-layer structure 5 having the bi-layer 7, the second cured layer 20(FIG. 1) includes particles 60 that can be biocidal particles 60, forexample that have a silver component, have a sulfur component, have acopper component, are a salt, are a silver sulfate salt or otherbiocidal particles, or include phosphors to form a biocidal second curedlayer 20 a. In an embodiment, the biocidal second cured layer 20 a has asurface 22 on a side of the biocidal second cured layer 20 a oppositethe first cured layer 10 and support 30 and portions of the particles 60extend beyond the surface 22 forming exposed particles 62. The particles60 can also have a distribution of sizes so that some of the particles60 are large particles 64 that can, but do not necessarily, extendbeyond the surface 22 and are therefore also exposed particles 62. Theparticles 60 are located within and between the indentations 80 of thestructure bi-layer 7 and include both the large particles 64 and theexposed particles 62.

In this embodiment, the second cured layer 20 (FIG. 1) is a biocidalsecond cured layer 20 a. By biocidal layer is meant herein any layerthat resists the growth of undesirable biological organisms, includingmicrobes, bacteria, or fungi or more generally, eukaryotes, prokaryotes,or viruses. In particular, the biocidal second cured layer 20 a inhibitsthe growth, reproduction, or life of infectious micro-organisms thatcause illness or death in humans or animals and especiallyantibiotic-resistant strains of bacteria. The biocidal second curedlayer 20 a is rendered biocidal by including particles 60 such as ionicmetals or metal salts in the biocidal second cured layer 20 a. Theparticles 60 reside in the biocidal second cured layer 20 a. In anembodiment, some of the particles 60 in the biocidal second cured layer20 a are exposed particles 62 that extend from the second-layer firstside 22 into the environment and can interact with any environmentalcontaminants or biological organisms in the environment. Exposedparticles 62 are thus more likely to be efficacious in destroyingmicrobes. In various embodiments, the particles 60 are silver or copper,are a metal sulfate, have a silver component, are a salt, have a sulfurcomponent, have a copper component, are a silver sulfate salt, orinclude phosphors. In an embodiment, the biocidal second cured layer 20a is thinner than the first cured layer 10 so that the second-layerthickness 26 is less than the first-layer thickness 16, thus reducingthe quantity of particles 60 that are required in the biocidal secondcured layer 20 a. In an alternative embodiment, the second-layerthickness 26 is greater than the first-layer thickness 16.

In an embodiment, the particles 60 are coated, for example with thematerial in the second cured layer 20 (FIG. 1).

In other embodiments, the biocidal second cured layer 20 a has athickness that is less than at least one diameter of one or more of theparticles 60, has a thickness that is less than a mean diameter of theparticles 60, or has a thickness that is less than the median diameterof the particles 60. Alternatively, the particles 60 have at least onediameter between 0.05 and 25 microns. In such embodiments, one or moreof the particles 60 will be exposed particles 62. If such exposedparticles 62 are biocidal, the exposed particles 62 can inhibit thegrowth or reproduction of microbes or destroy any microbes on thesurface of the biocidal second cured layer 20 a. In yet anotherarrangement, the biocidal second cured layer 20 a is greater than orequal to 0.5 microns thick and less than or equal to 20 microns thick orthe first cured layer 10 on the support 30 includes particles 60 (notshown in FIG. 3).

The indentations 80 form a topographical non-planar layer in the secondcured layer 20, the patterned second cured layer 21, or the biocidalsecond cured layer 20 a that is not smooth and is inhospitable to thegrowth and reproduction of microbes. In yet another embodiment, thefirst or second cured layers 10, 20, the patterned second cured layer21, or the biocidal second cured layer 20 a have a hydrophobic surface,for example by providing a roughened surface either by imprinting or bya treatment such as sandblasting or exposure to energetic gases orplasmas.

Referring to FIGS. 4A to 4F and FIG. 7, a method of the presentinvention includes making the imprinted multi-layer structure 5 havingthe support 30 (FIG. 4A) in step 100 (FIG. 7). A first curable layer 13including a first material is located on or over the support 30 (FIG.4B) in step 105. A second curable layer 23 including a second materialdifferent from the first material is located on or over the firstcurable layer 13 in step 110 (FIG. 4C) before the first curable layer 13is cured. The first curable layer 13 and the second curable layer 23 areformed in various ways, including extrusion or coating, for example spincoating, curtain coating, or hopper coating, or other methods known inthe art. In other embodiments of the present invention, locating thefirst curable layer 13 includes laminating a first curable material onor over the support 30 or locating the second curable layer 23 includeslaminating a second curable material on or over the first curable layer13.

The first curable layer 13 and the second curable layer 23 are imprintedin a single step 125 with an imprinting stamp 90 having a structure witha structure depth 46 greater than the second layer thickness 26 of thesecond curable layer 23 (FIG. 4D) and then cured in a single step 130,for example with heat or radiation 92 to form the first cured layer 10and the second cured layer 20 (FIG. 4E). The imprinting stamp 90 isremoved in step 135 to form an imprinted structured bi-layer 7 with astructure depth 46 greater than the second-layer thickness 26 of thesecond cured layer 20 (FIG. 4F) to form the structured bi-layer 7 of theimprinted multi-layer structure 5 of the present invention.

An imprinted multi-layer structure 5 having the structured bi-layer 7 ofthe present invention has been constructed in a method of the presentinvention using cross-linkable materials such as curable resins (forexample using SU8 at suitable viscosities and PEDOT) coated on a glasssurface and imprinted using a PDMS stamp to form micro-structures in thebi-layer 7. Electrically conductive PEDOT layers have been patterned toform circuit or wiring patterns and conductive links have been locatedand cured in the micro-channels to form cured conductive wires.

Referring further to FIG. 7 in an embodiment of the present invention,the surface 8 of the structure 40 is identified in step 150. The surface8 is a surface which it is desired to keep free of microbes, for examplea wall, floor, table top, door, handle, knob, cover, or device surface,especially any surface 8 found in any type of medical institution. In anembodiment, the surface 8 is planar; in another embodiment, the surface8 is non-planar. In step 155, an adhesive is located, for example on thesurface 8 or on the side of the support 30 opposite the first curedlayer 10, to form the adhesive layer 50. The support 30 is adhered tothe surface 8 in step 160. In a further embodiment, the support 30,first cured layer 10, and second cured layer 20 are heated to shrink theimprinted multi-layer structure 5 on the surface 8 if the surface 8 isnon-planar. In an embodiment, the heating step (not shown separately) isalso the adhesion step 160 and a separate adhesive layer 50 is notnecessary or used. In an embodiment, the second cured layer 20 isthinner than the first cured layer 10.

In another embodiment, referring to FIG. 2, the third cured material 42,for example a liquid conductive ink, is located in the indentations 80of the bi-layer 7, for example by coating the surface and indentations80 of the second cured layer 20 with a liquid conductive ink, wiping thesurface of the second cured layer 20 to remove excess liquid conductiveink from the surface but not the indentations 80, and curing the liquidconductive ink in the indentations 80 to form an electrical conductorsin each of the indentations 80. Such coating, wiping, and curing methodsand materials are known in the art.

Referring next to FIGS. 5A to 5F and to FIG. 7 again, a dispersion ofparticles 60 is formed in step 120 in the second cross-linkable materialfor example before locating a biocidal second curable layer 23 a on orover the first curable layer 13 (FIG. 5A). In an embodiment, adispersion of particles 60 is formed in a carrier such as a liquid, forexample a curable resin, in a container 66. Making and coating liquidswith dispersed particles is known in the art. A dispersion havingantimicrobial particles 60 has been made. The dispersion includedthree-micron silver sulfate particles milled in an SU8 liquid to anaverage particle size of one micron, and successfully coated on glassand tested with E. coli bacteria. In an alternative, the biocidal secondcurable layer 23 a is made separately and laminated on or over the firstcurable layer 13.

After steps 100 and 105 of FIG. 7 and as shown in FIGS. 4A and 4B, thedispersion is coated or a layer laminated on the first curable layer 13to form the biocidal second curable layer 23 a (FIG. 5B). The silversulfate particle dispersion noted above was spin-coated on the glasssupport 30, cured, and tested for anti-microbial efficacy. As shown inFIG. 5C, the first curable layer 13 and biocidal second curable layer 23a (the biocidal second curable layer 23 a including the particles 60) onthe support 30 are imprinted in step 125 with the stamp 90 and curedwith radiation 92 in step 130 to form the first cured layer 10 andbiocidal second cured layer 20 a. In an embodiment, the curing step 130includes cross-linking the first curable layer 13 to the biocidal secondcurable layer 23 a. The stamp is removed in step 135 to form theimprinted multi-layer structure 5 having the structured bi-layer 7 shownin FIG. 5D. Imprinting methods using stamps are known in the art.

As shown in FIG. 5E, in a further embodiment of the present invention, aportion of the biocidal second cured layer 20 a is removed in step 140,for example by etching or using energetic particles 94 such as withplasma etching, reactive plasma etching, ion etching, or sandblastingthe first cured layer 10 or the biocidal second cured layer 20 a. Such aremoval treatment can remove any coating over the exposed particles 62and further expose the exposed particles 62 to the environment.Alternatively, particles 60 are exposed by washing the first or secondcured layer 10, 20. In an embodiment, the second-layer thickness 26Bafter the removal step 140 is less than the second-layer thickness 26A(FIG. 5D) before the removal step 140.

As shown in FIG. 5F, the result of the process is an imprintedmulti-layer structure 5 with a structured bi-layer 7 including firstcured layer 10 and biocidal second cured layers 20 a on the support 30.The biocidal second cured layer 20 a includes particles 60, includinglarge particles 64 and exposed particles 62 in a second material, forexample a second cured material. A coating of silver sulfate particlesdispersed in SU8 has been exposed to plasma to reduce the coatingthickness and further expose the particles 60 to the environment.

In an embodiment, the first cured layer 10 includes a firstcross-linkable material, the biocidal second cured layer 20 a includes asecond cross-linkable material and the curing step 130 cross-links thefirst cross-linkable material to the second cross-linkable material. Inanother embodiment, the first material includes a first cross-linkablematerial and the second material includes a second cross-linkablematerial that is different from the first cross-linkable material andthe curing step 130 cross-links the first cross-linkable material to thesecond cross-linkable material. Alternatively, the first materialincludes a first cross-linkable material, the second material includes asecond cross-linkable material that is the same as the firstcross-linkable material, and a third material is included in either thefirst material or the second material but not both the first and secondmaterials and the curing step 130 cross-links the first cross-linkablematerial to the second cross-linkable material.

In another embodiment of the present invention, referring back to FIG.1, the first cured layer 10 and the second cured layer 20 are notnecessarily cross-linked. In such an embodiment, the biocidal imprintedmulti-layer structure 5 includes the support 30 and the bi-layer 7having a topographical structure on or over the support 30. Thestructured bi-layer 7 includes the first cured layer 10 on or over thesupport 30 and the second cured layer 20 on or over the first curedlayer 10 on a side of the first cured layer 10 opposite the support 30.The structure of the structured bi-layer 7 has at least one structuredepth 46 that is greater than the second-layer thickness 26 of thesecond cured layer 20. In an embodiment, multiple biocidal particles 60are located only in the second cured layer 20.

Similarly, according to a method of the present invention and referringagain to FIG. 7 and FIGS. 5A-5F, a method of making a biocidal imprintedmulti-layer structure 5 includes providing the support 30 in step 100,locating the first curable layer 13 on the support 30 in step 105,forming a dispersion of multiple biocidal particles 60 in step 120,locating the biocidal second curable layer 23 a on the first curablelayer 13 in step 110 using the dispersion, the biocidal second curablelayer 23 a having multiple biocidal particles 60 dispersed within thebiocidal second curable layer 23 a, imprinting the first curable layer13 and the biocidal second curable layer 23 a in a single step with animprinting stamp 90 having a structure with a depth greater than thethickness of the biocidal second curable layer 23 a in step 125, curingthe first curable layer 13 and the biocidal second curable layer 23 a ina single step to form the first cured layer 10 and the biocidal secondcured layer 20 a in step 130, and removing the imprinting stamp 90 instep 135.

In yet another embodiment of the present invention, not separatelyillustrated, the layer on a side of the first cured layer 10 oppositethe support 30 (e.g. corresponding to the second cured layer 20) is asecond layer that is not necessarily a cured layer and is notcross-linked. In various embodiments, this second layer isnon-conductive, conductive, pattern-wise conductive, or include biocidalparticles 60. The second layer is in a spatial relationship to the firstcured layer 10 on a side of the first cured layer 10 opposite thesupport 30. The structure of the structured bi-layer 7 has at least onestructure depth 46 that is greater than the second-layer thickness 26 ofthe second layer. Multiple biocidal particles 60 are located only in thesecond layer. In an embodiment the particles 60 are fixed in, fixed on,or adhered to the cross-linked material in the first cured layer 10.

Referring to the sequential structures illustrated in FIGS. 6A-6D andthe flow charts of FIGS. 8A and 8B, an alternative method of making abiocidal bi-layer 7 includes providing the support 30 in step 100 andlocating the first curable layer 13 on the support 30 in step 105 (asshown in FIG. 7). Referring to FIG. 8A and FIG. 6A, a biocidal secondlayer 25 a is located on or over the first curable layer 13. Thebiocidal second layer 25 a includes multiple biocidal particles 60located within the second cured layer 20.

Referring specifically to FIG. 8A in an embodiment, the biocidalparticles 60 are provided in step 300 and then mechanically distributedover the first curable layer 13 in step 305. For example, the particlesare agitated within a container or on a surface to form a uniformdistribution of particles 60 and then released above the first curablelayer 13 so that the particles 60 fall under the influence of gravityonto the first curable layer 13. Ways to distribute particles 60 over alayer are known in the art. The distribution of particles 60 on thefirst curable layer 13 forms the biocidal second layer 25 a on the firstcurable layer 13 (equivalent to step 110 in FIG. 7) as shown in FIG. 6A.

Referring specifically to FIG. 8B, in an alternative embodiment,particles 60 are provided in step 300 and dispersed into an evaporableliquid in step 310 (and as shown in step 120 in FIG. 7) to form adispersion. This dispersion is distinguished from that of FIG. 5A inthat is evaporable rather than curable. The dispersion is coated on orover the first curable layer 13 in step 320, for example by spincoating, hopper coating, curtain coating or other methods known in theart. The dispersion is then dried in step 330 (and as shown in step 110of FIG. 7), for example by heating or drying without curing the firstcurable layer 13 or at least without completely curing the first curablelayer 13, to form the biocidal second layer 25 a. The biocidal secondlayer 25 a is formed as a layer of particles 60 on the surface of thefirst curable layer 13 as shown in FIG. 6A.

The first curable layer 13 and the biocidal second layer 25 a are thenimprinted with an imprinting stamp having a structure with a depthgreater than the thickness of the second curable layer in a single stepin step 125, referring now to FIG. 7 and as shown in FIG. 6B. As shownin FIG. 6C, the particles 60 of the biocidal second layer 25 a areimpressed by the imprinting stamp into the first curable layer 13. Inone embodiment of the present invention, the particles 60 of thebiocidal second layer 25 a are impressed completely into the firstcurable layer 13 so that the biocidal second layer 25 a is a part of thefirst curable layer 13 (as shown in FIG. 6C) and is transformed into thebiocidal second curable layer 23 a. In this case, the biocidal secondcurable layer 23 a overlaps with the first curable layer 13 so that theentire biocidal second curable layer 23 a is in common with a portion ofthe first curable layer 13. In an alternative embodiment of the presentinvention shown in FIG. 6D, at least some of the particles 60 of thebiocidal second layer 25 a (FIG. 6B) are impressed only part way intothe first curable layer 13 so that the biocidal second curable layer 23a overlaps a part of the first curable layer 13. The exposed particles62 extending beyond the surface of the first curable layer 13 (as shownin FIG. 6D) form the biocidal second layer 25 a and does not overlapwith the first curable layer 13.

In step 130, the first curable layer 13 and the second curable layer 23(or biocidal second curable layer 23 a) is cured in a single step toform the first cured layer 10 and second cured layer 20 or biocidalsecond cured layer 20 a and fix the particles 60 in the bi-layer 7. Ifthe first curable layer 13 includes a cross-linkable material, the step130 of curing the first curable layer 13 and the second curable layer 23or biocidal second curable layer 23 a fixes the particles 60 within thecross-linkable material. In step 135, the imprinting stamp is removed.Optionally, a portion of the second layer is removed in step 140 and thebi-layer 7 adhered to the surface 8.

In the embodiments of FIGS. 8A and 8B, the biocidal second curable layer23 a with the particles 60 is considered to overlap with the firstcurable layer 13 and the first cured layer 10 so that a portion of thefirst curable layer 13 is in common with the second curable layer 23 orbiocidal second curable layer 23 a. In an alternative understanding, aportion of the first curable layer 13 is converted into the secondcurable layer 23 or biocidal second curable layer 23 a when theparticles 60 are impressed into the first curable layer 13 so that thefirst curable layer 13 is reduced in thickness and at least a portion ofthe second curable layer 23 or biocidal second curable layer 23 a iscured. These understandings of the first curable layer 13 and secondlayer (second curable layer 23, biocidal second curable layer 23 a, orbiocidal second layer 25 a) and understanding of the first cured layer10 and second layer (second cured layer 20, biocidal second cured layer20 a, biocidal second layer 25 a) are equivalent in practice, since theyresult in a layer of particles at least partially embedded in the firstcured layer 10. Essentially, the second curable layer 23, biocidalsecond curable layer 23 a, and biocidal second layer 25 a are allembodiments of a second layer formed on first curable layer 13 beforethe first curable layer 13 is cured to form the first cured layer 10.Likewise, the second cured layer 20, biocidal second cured layer 20 a,and biocidal second layer 25 a are all embodiments of a second layerformed on first cured layer 10 after the first curable layer 13 is curedto form the first cured layer 10. To illustrate these differentunderstandings of the first cured layer 10 and the biocidal second curedlayer 20 a or biocidal second layer 25 a, a dashed line demarcates thetwo layers in FIGS. 6C and 6D. Whether the layers are considered to beseparate layers or to overlap is a matter of perspective having littlepractical consequence.

Thus, in various embodiments, a portion of a second layer is in commonwith a portion of the first cured layer 10 or an entire second layer isin common with a portion of the first cured layer 10. In variousembodiments, the second layer is a curable or cured layer, isnon-conductive, is conductive, or includes biocidal particles. In yetanother embodiment, cured portions of the second layer are removed (step140) so that only the particles 60 remain adhered to the first curedlayer 10 so that none of the second layer is in common with a portion ofthe first cured layer 10 (not shown).

In yet another embodiment, the first cured layer 10 or the second curedlayer 20, biocidal second cured layer 20 a, or biocidal second layer 25a have a hydrophobic surface, for example by providing a roughenedsurface either by imprinting or by a treatment such as sandblasting orexposure to energetic gases or plasmas or from the presence of thebiocidal particles 60.

In a further embodiment of the present invention, the first cured layer10, the second cured layer 20, the biocidal second cured layer 20 a, orthe support 30 is or includes a heat-shrink film, for examplepolyolefin, polyvinylchloride, polyethylene, or polypropylene. Any ofthe first cured layer 10, the second cured layer 20, the biocidal secondcured layer 20 a, or the support 30 can include cross linking materialsthat are cross linked for example by radiation or heat to providestrength.

Referring to FIG. 9, in various embodiment of the present invention, anyof the biocidal bi-layers 7 or the biocidal imprinted multi-layerstructures 5 described above, including those of FIG. 3, 5D, 5F, or 6Dis located on a surface 8 in step 200 and observed over time in step205. Periodically or as needed, the imprinted multi-layer structure 5 iscleaned in step 210, for example by washing with water or with acleaning fluid, or wiping the multi-layer structure 5. The imprintedmulti-layer structure 5 is repeatedly observed (step 205) and cleaned(step 210) until it is no longer efficacious for its intended purpose.The biocidal imprinted multi-layer structure 5 is replaced, removed, orcovered over in step 220.

In an embodiment, the cleaning step removes dead micro-organisms or dirtfrom the surface 22 of the biocidal second cured layer 20 a so that thebiocidal efficacy of the particles 60 is improved in the absence of thedead micro-organisms or dirt. Useful cleaners include hydrogen peroxide,for example 2% hydrogen peroxide, water, soap in water, or acitrus-based cleaner. In an embodiment, the 2% hydrogen peroxidesolution is reactive to make oxygen radicals that improve the efficacyof particles 60. In various embodiments, cleaning is accomplished byspraying the surface 22 of the biocidal second cured layer 20 a with acleaner and then wiping or rubbing the surface 22. The cleaner candissolve the biocidal second cured layer 20 a material (e.g. crosslinking material) and the wiping or rubbing can remove dissolvedmaterial or abrade the surface 22 of the biocidal second cured layer 20a to expose other particles 60 or increase the exposed surface area ofexposed particles 62.

Alternatively, the cleaning or washing step 210 refreshes the particles60, for example by a chemical process, to improve their biocidalefficacy. This can be done, for example, by ionizing the particles 60,by removing oxidation layers on the particles 60, or by removingextraneous materials such as dust from the particles 60.

Replacement of the biocidal second cured layer 20 a or biocidal secondlayer 25 a can proceed in a variety of ways. In one embodiment, anotherbiocidal imprinted multi-layer structure 5 is simply located over thebiocidal imprinted multi-layer structure 5. Thus, the biocidalmulti-layer structure 5 becomes the structure 40 and another biocidalimprinted multi-layer structure 5 is applied to the structure 40, forexample with an adhesive layer 50 (FIG. 1). In another embodiment, thebiocidal imprinted multi-layer structure 5 is removed and anotherbiocidal imprinted multi-layer structure 5 put in its place. As shown inFIG. 1, the support 30 is adhered to the structure 40 with an adhesivelayer 50. Chemical or heat treatments are applied to the biocidalmulti-layer structure 5 to loosen, dissolve, or remove the adhesivelayer 50 so the biocidal imprinted multi-layer structure 5 can beremoved and another adhesive layer 50 applied to the structure 40 toadhere the biocidal imprinted multi-layer structure 5 to the structure40. In an embodiment, the biocidal imprinted multi-layer structure 5 ispeeled from the structure 40 and another biocidal imprinted multi-layerstructure 5 having an adhesive layer 50 is adhered to the structure 40.

Alternatively, portions of the biocidal imprinted multi-layer structure5 are removed, for example at least a portion of the biocidal secondcured layer 20 a is mechanically separated from the first cured layer10. In an embodiment, the biocidal second cured layer 20 a is peeledfrom the first cured layer 10. Alternatively, the biocidal second curedlayer 20 a is abraded and removed by abrasion from the first cured layer10. In another embodiment, the biocidal second cured layer 20 a ischemically separable from the first cured layer 10 or chemicallydissolvable in a substance that does not dissolve the first cured layer10. In a useful embodiment, a substance that chemically separates thebiocidal second cured layer 20 a from the first cured layer 10 or thatchemically dissolves the biocidal second cured layer 20 a is a cleaningagent. In an embodiment, the biocidal second cured layer 20 a isrepeatedly cleaned, for example by spraying the biocidal second curedlayer 20 a with a cleaning agent and then rubbing or wiping the biocidalsecond cured layer 20 a, and at each cleaning a portion of the biocidalsecond cured layer 20 a is removed to gradually expose the first curedlayer 10.

In another embodiment of the present invention, fluorescent orphosphorescent materials are included in the second cured layer 20 orbiocidal second cured layer 20 a and are illuminated. The fluorescent orphosphorescent materials respond to ultra-violet, visible, or infraredillumination and emit light that can be seen or detected and compared toa threshold emission value. Thus, the continuing presence of the secondcured layer 20 or biocidal second cured layer 20 a is observed. Whenlight emission in response to illumination is no longer present at adesired level, the second cured layer 20 or biocidal second cured layer20 a is replaced.

The present invention is useful in a wide variety of environments and ona wide variety of surfaces 8, particularly surfaces 8 that arefrequently handled by humans. The present invention can reduce themicrobial load in an environment and is especially useful in medicalfacilities.

The invention has been described in detail with particular reference tocertain embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

PARTS LIST

-   5 multi-layer structure-   7 bi-layer-   8 surface-   10 first cured layer-   13 first curable layer-   16 first-layer thickness-   20 second cured layer-   20 a biocidal second cured layer-   21 patterned second cured layer-   21 a conductive portion-   21 b non-conductive portion-   22 surface-   23 second curable layer-   23 a biocidal second curable layer-   25 a biocidal second layer-   26, 26A, 26B second-layer thickness-   30 support-   36 support thickness-   40 structure-   42 third cured material-   46 structure depth-   50 adhesive layer-   52 binder primer-   60 particle-   62 exposed particle-   64 large particle-   66 container-   80 indentations-   90 stamp-   92 radiation-   94 energetic particles-   100 provide support step-   105 locate first layer step-   110 locate second layer step-   120 form dispersion step-   125 imprint first and second layers step-   130 cure first and second layers step-   135 remove stamp step-   140 remove second layer portion step-   150 identify surface step-   155 locate adhesive step-   160 adhere support to surface step-   200 locate structure step-   205 observe structure step-   210 clean structure step-   220 replace biocidal layer step-   300 provide particles step-   305 mechanically distribute particles on first layer step-   310 disperse particles in evaporable liquid step-   320 coat dispersion on first layer step-   330 evaporate liquid to form second layer step

The invention claimed is:
 1. A method of making a multi-layer biocidalstructure, comprising: providing a support; providing a first curablelayer on the support; providing a second curable layer on and incontinuous contact with the first curable layer, the second curablelayer having multiple biocidal particles dispersed in the second curablelayer, the second curable layer having a thickness; imprinting the firstcurable layer and the second curable layer in a single step with animprinting stamp having a structure with a depth greater than thethickness of the second curable layer; curing the first curable layerand the second curable layer in a single step to form a first curedlayer and a second cured layer that completely covers the first curedlayer; and removing the imprinting stamp.
 2. The method of claim 1,wherein the first curable layer includes a first cross-linkablematerial, the second curable layer includes a second cross-linkablematerial, and the step of curing cross links the first cross-linkablematerial to the second cross-linkable material.
 3. The method of claim2, wherein the first cross-linkable material is the same material as thesecond cross-linkable material.
 4. The method of claim 1, whereinlocating the first curable layer includes coating or laminating a firstcurable material on or over the support.
 5. The method of claim 1,wherein locating the second curable layer includes coating or laminatinga second curable material on or over the first curable layer.
 6. Themethod of claim 1, further including etching, plasma etching, reactiveplasma etching, ion etching, or sandblasting the first cured layer orthe second cured layer.
 7. The method of claim 6, further includingremoving a portion of the second cured layer to expose at least aportion of the surface of at least one of the particles.
 8. The methodof claim 1, further including forming a dispersion of biocidal particlesin the second curable material before providing the second curable layeron or over the first curable layer.
 9. The method of claim 1, whereinthe second curable layer is thinner than the first curable layer. 10.The method of claim 1, wherein the second curable layer is thinner thana mean or median diameter of the particles.
 11. The method of claim 1,wherein the second curable layer is thicker than a mean or mediandiameter of the particles.
 12. The method of claim 1, further includingwashing the first cured layer or the second layer.
 13. The method ofclaim 1, wherein the first cured layer has a different color than thesecond cured layer.